1. Technical Field
The invention relates to spectrum sensors and angle restriction filters.
2. Related Art
Spectrum sensors are used in the medical, agricultural and environmental fields for diagnosing and examining objects. For example, in the medical field, a pulse oximeter is used to measure the oxygen saturation of blood, using light absorption of hemoglobin. Also, in the agricultural field, a saccharometer is used to measure the concentration of sugar content of fruits, using light absorption of sugar.
For example, Japanese Laid-open Patent Application JP-A-6-129908 describes a spectroscopic imaging sensor that restricts incident angles of light with an optical fiber that optically connects between a dichroic filter and a photovoltaic converter device, thereby restricting the transmission wavelength band of light to the photovoltaic converter device.
However, the spectrum sensors of related art entail a problem in that it is difficult to reduce their size. Therefore, placement of numerous sensors in a desired location or permanent placement thereof is difficult.